(1) Field of the Invention
The invention relates generally to data networks and, more specifically, to network system synchronization.
(2) Description of the Related Art
In a network, data passes through network nodes. The network nodes allow data to be routed to their destinations. Such network nodes often include a plurality of line cards and one or more control cards. The line cards are coupled to a plurality of lines, while the control cards control the line cards.
In the past, the control of line cards relied heavily on execution of software. Both the line cards and the control cards contained processors that executed the software. The action of transitioning a line card from an active state to an inactive state and transitioning another line card from the inactive state to the active state raised a number of issues. One issue is that all of the software entities of the different components needed to communicate to each other that a line card redundancy switch was in progress. Software needed to be executed on a control card to determine how to deselect the timing information from the first line card and select timing information from the second line card. The software used to deselect and select timing information has generally been complex, and its execution has required a significant amount of time during which the reference signal was indeterminate. Such indeterminate signals have compromised the quality of the reference signal in the control card, introducing effects such as jitter.
Thus, a method and apparatus is needed to reduce the time and complexity previously required to change a source of timing information when transitioning between activation of multiple line cards. Such a method and apparatus is needed to avoid degradation of network synchronization that can result from the previous techniques.